This invention relates generally to electric resistance heaters and more specifically to an abnormal condition detection system for use in electrical resistance heaters, wherein the system will automatically shut-off the heater upon detection of an abnormal condition and simultaneously generate an alarm warning.
Safety considerations with regard to electric appliances and particularly with regard to electrical resistance type space heaters have led to the incorporation of various safety features in such heaters. Two primary safety features which have been included in prior designs are systems for effectively shutting off the electrical heater if the temperature of the heating element exceeds a predetermined threshold temperature and systems for shutting off the electric heater if the electric heater is tipped over or tilted beyond a predetermined upright or level position. These two safety features are desirable since either of these conditions may constitute a serious safety hazard if the heater is not effectively disabled upon the occurrence of these events.
An example of an electric space heater safety system which includes a gravity actuated tip-over switch is disclosed in U.S. Pat. No. 3,637,981 (Swimmer). The tip-over switch includes a weighted member which maintains a vertical position resulting from the force of gravity. An operating member attached to the weighted member urges a pair of electrical contacts apart, thereby opening the circuit for the heating element when the heater is tilted beyond a predetermined angle.
U.S. Pat. Nos. 3,201,548 (Mertler) and 3,271,546 (Chesnut) each disclose systems including a combined thermostat and tip-over switch which may be used with electrical appliances such as with electrically heated appliances. In the systems disclosed by these two references, the appliance is de-energized by the separation of a single set of electrical contacts. The systems include a gravity actuated pendulum type tip-over switch to separate the electrical contacts when the appliance is tilted beyond a predetermined level upright position. The thermostat/tip-over switch also includes a set of bimetallic blades which are responsive to temperature changes. The bimetallic blades are used to separate the contacts when the temperature exceeds a predetermined adjustable level.
Although the above described devices will effectively disable the heating element of an electrical resistance type heater when the heater is either tilted beyond a predetermined tilt angle or when the heater exceeds a predetermined operating temperature, these devices do not generally provide any indication to the user that an abnormal condition has occurred. It is desirable to provide the user with a warning signal in order for the user to take appropriate steps to correct any hazardous condition which may arise due to the abnormal operation of such heaters.
To this end, the arrangement disclosed in U.S. Pat. No. 4,755,653 (Townsend et al.) comprises a heater assembly which includes an alert indicator. The alert indicator warns the user when the heater either exceeds a predetermined safe operating temperature or is tilted beyond a safe tilt angle. The alert indicator includes a buzzer and a pilot light to provide a visual and aural warning to the user when an abnormal condition has occurred. The buzzer and pilot light are activated by a tip-over switch which is normally in an open condition when the heater is in a normal upright level position. When the heater is tilted, the tip-over switch closes to activate the buzzer and pilot light. A thermostat which includes a second tip-over switch is used to disable the heating element when the heater is tilted beyond a predetermined level position. The system also includes a temperature limit control which disables the heating elements when the temperature exceeds a predetermined temperature. The temperature limit control includes a single-pole, double-throw switch with two sets of contacts. A first set of contacts, normally in a closed position, enables the heating elements when the heater is operating below the predetermined temperature. A second set of contacts, normally in an open position, closes to activate the buzzer and pilot light when the heater exceeds the predetermined temperature.
Although the system disclosed by Townsend et al provides the desired alarm warning, the system is not without limitations. Since the system includes two separate tip-over switches, one to disengage the heating elements and another to activate the alarm, any variance between the settings of the two tip-over switches may reduce the effectiveness of the alarm system. If the two tip-over switches operate at different angles from one another, it is possible that the heating elements may be disabled while the alarm system is not actuated or that the alarm may be actuated without the heating element being disabled. In either case, the effectiveness of the alarm system is reduced. Further, it is desirable to minimize the number of tip-over switches used in a heater for purposes of manufacturing economy.
It is therefore desirable to provide a system which includes an alarm system wherein the alarm system will be actuated by the same tip-over switch which disables the heating element. It is also desirable to provide a system wherein the alarm will also be actuated by a temperature limit control switch which disables the heating element of the heater.
Therefore, in view of the above, it is a general object of the present invention to provide a heater assembly wherein the same tip-over switch disables the resistive heating element and actuates an alarm system.
It is a further object of the present invention to provide a system which requires only a single tip-over switch to disengage the heating element and actuate an alarm system.
It is still a further object of the present invention to provide a heater assembly wherein a temperature limit control switch disables the heating element and simultaneously actuates an alarm system.